Blade modification method, impeller modification method and impeller

Abstract

The invention discloses a blade remodeling method, an impeller remodeling method and an impeller. The blade modification method comprises the steps that a model of a reference blade is obtained, 2n + 1 spanwise surface contour lines are drawn on the model, the 2n + 1 spanwise surface contour lines are sequentially arranged from the first end, connected with a hub, of the reference blade to the second end, connected with a rim, of the reference blade, the first spanwise surface contour line is the side line of the end face of the first end, and the second spanwise surface contour line is the side line of the end face of the second end; the (2n + 1) th spanwise surface contour line is the side line of the end surface of the second end; the overall space angle from the second spanwise surface contour line to the (2n + 1) th spanwise surface contour line is increased in the rotating direction of the reference blade; and fitting a smooth curved surface by adopting the first to (2n + 1) th spanwise surface contour lines, wherein the smooth curved surface is used as the outer contour of the modified blade. According to the method, the internal flow field of the impeller can be quickly and effectively optimized, and the effects of restraining or delaying rotating stall and cavitation occurrence points and improving the unsteady and unstable flow phenomenon in a unit are achieved.

Description

Technical Field

[0001] The present invention relates to fluid machinery technology, and in particular to a blade modification method, an impeller modification method and an impeller. Background Art

[0002] Among renewable energy sources, hydropower has always ranked first in annual power generation, and the development of pumped storage with rapid and large-capacity regulation capabilities has become an indispensable key measure in my country's energy development strategy. However, as pumped storage develops towards large capacity and ultra-high head, unit safety issues caused by flow instability have become a huge obstacle to the development of pumped storage technology internationally.

[0003] Rotating stall and cavitation flow are two common unstable flow phenomena in fluid machinery. When a vane pump with a diffuser operates in an off-center condition, it is easy to induce rotating stall in the blade flow due to the increase in the blade inlet angle of attack and the static-dynamic interference effect. When stall occurs, its propagation speed in the blade flow channel is much lower than the impeller rotation speed, inducing low-frequency, high-amplitude water pressure pulsation. At the same time, when the inlet ambient pressure decreases, it is easy to induce cavitation flow at the inlet and blade tip clearance, which directly affects the pump performance and stable operation. During the actual operation of the unit, the cavitation flow induced by the blade tip clearance is closely related to the rotating stall in the flow channel between the blades, and there is a strong intrinsic correlation.

[0004] In order to suppress the rotating stall group induced inside the vane pump and improve its cavitation performance, some optimization modification methods can be sought in engineering: such as adjusting the blade inlet shape to improve its cavitation performance, adjusting the guide vane opening, and expanding the gap in the bladeless area to suppress the propagation of the rotating stall group.

[0005] However, the interaction mechanism between rotating stall and cavitation flow in time and space has not yet been fully and systematically understood, especially the guiding conclusions for improving pump performance are not comprehensive enough. At present, some optimization algorithm-based methods are often used to evaluate the parameters of impeller blades, but this method requires more examples and data to improve the accuracy of optimization, and the time cost and number of examples are relatively large.

[0006] In order to better meet the requirements of pumped storage unit operation stability, it is urgent to further explore the dynamic characteristics and formation mechanism of rotating stall and cavitation flow induced in vane pump equipment, and seek a universal design optimization method to improve unstable flow. At present, there is no universal modification method on the market to improve the rotating stall and cavitation flow of vane pumps from the source. Summary of the invention

[0007] Based on the mechanism of rotational stall and cavitation flow induction of vane pump, the present invention provides a blade modification method for suppressing rotational stall between blades and improving cavitation performance. The present invention can quickly and effectively optimize the internal flow field of the impeller: suppress or delay the occurrence of rotational stall and cavitation, and improve the unsteady and unstable flow phenomenon inside the unit. The blade modification method specifically includes:

[0008] Obtain a model of a reference blade, and draw 2n+1 spanwise surface contour lines on the model, wherein the 2n+1 spanwise surface contour lines are arranged in sequence from a first end of the reference blade connected to a hub to a second end of the reference blade connected to a rim, wherein the first spanwise surface contour line is an edge line of an end surface of the first end, the 2n+1 spanwise surface contour line is an edge line of an end surface of the second end, and 2n-1 spanwise surface contour lines are evenly drawn on the model surface of the reference blade between the first spanwise surface contour line and the 2n+1 spanwise surface contour line;

[0009] The overall spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line is increased toward the rotation direction of the reference blade, and the increase amount of the spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line is increased in sequence;

[0010] A smooth surface is fitted using the 1st to 2n+1th spanwise surface contour lines, and the smooth surface serves as the outer contour of the modified blade.

[0011] In an illustrative embodiment, the amount of increase of the spatial angle from the second spanwise surface contour line to the 2n+1th spanwise surface contour line increases in sequence in an arithmetic progression.

[0012] In an exemplary embodiment, the increase in the spatial angle of the 2n+1th spanwise surface contour line is greater than or equal to 28°.

[0013] In an exemplary embodiment, when the spatial angle of each spanwise surface contour line is increased, the spatial angle of each point of the spanwise surface contour line from the leading edge to the trailing edge increases uniformly.

[0014] In an exemplary embodiment, the 2nd to 2n-1th spanwise surface contour lines evenly divide the model of the reference blade into 2n segments in the direction from the first end to the second end.

[0015] In an illustrative embodiment, a rectangular coordinate system is established in a two-dimensional plane perpendicular to the rotation axis of the blade, the intersection of the rotation axis of the blade and the two-dimensional plane is the origin of the coordinate system, a horizontal axis X passing through the origin is set in the two-dimensional plane, and the spatial angle of any point on the spanwise surface contour line is the angle between the vector of the projection from the origin to this point on the two-dimensional plane and the horizontal axis X.

[0016] In an illustrative embodiment, the position of the first spanwise surface contour line remains unchanged.

[0017] This embodiment also proposes an impeller modification method, which includes the steps of the blade modification method as described above.

[0018] This embodiment also provides an impeller, which includes a blade, and the blade adopts the smooth curved surface obtained by the blade modification method as described above as the outer contour.

[0019] This blade modification method has the following advantages:

[0020] 1. The modification method is simple. The blade model modification can be completed by simply adjusting the leading edge and trailing edge space angles of the blade's different spanwise contour lines, which greatly simplifies the optimization process and improves production efficiency and work reliability;

[0021] 2. Wide applicability. Most existing flow optimization technologies attempt to modify the flow at the leading edge of the blade or in the bladeless area. At the same time, the interaction between multiple factors must be considered, and the process is relatively complicated. This application changes the relative position of the blade in space along the span direction, thereby changing the distribution characteristics of the flow in space, so as to achieve the effect of suppressing or delaying the rotational stall and the initiation of cavitation flow. This blade modification method can be widely used in the flow enhancement of vane pumps with diffusers;

[0022] 3. The axial flow channel of the blade itself, the inlet and outlet placement angles, and the wrap angles of the contour lines of each spanwise surface do not change, that is, the design operating point of the impeller itself does not change.

[0023] Other features and advantages of the present application will be described in the following description. Other advantages of the present application can be realized and obtained through the solutions described in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide an understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0025] Figure 1 This is a three-dimensional schematic diagram of an impeller before blade modification in an embodiment of the present application;

[0026] Figure 2 is a perspective schematic diagram of an impeller before blade modification in an embodiment of the present application;

[0027] Figure 3 is a schematic diagram of the blade profile space angle;

[0028] Figure 4 This is a schematic diagram of the impeller forward inclination angle after the blades are modified;

[0029] Figure 5 It is a schematic diagram of an impeller with modified blades in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The present application describes multiple embodiments, but the description is exemplary rather than restrictive, and it is obvious to those skilled in the art that there may be more embodiments and implementations within the scope of the embodiments described in the present application. Although many possible feature combinations are shown in the drawings and discussed in the specific embodiments, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with any other feature or element in any other embodiment, or may replace any other feature or element in any other embodiment.

[0031] The present application includes and contemplates combinations of features and elements known to those of ordinary skill in the art. The embodiments, features and elements disclosed in the present application may also be combined with any conventional features or elements to form a unique invention scheme. Any features or elements of any embodiment may also be combined with features or elements from other invention schemes to form another unique invention scheme. Therefore, it should be understood that any feature shown and / or discussed in the present application may be implemented individually or in any appropriate combination. Therefore, except for the limitations made according to the attached claims and their equivalents, the embodiments are not subject to other restrictions. In addition, various modifications and changes may be made within the scope of protection of the attached claims.

[0032] In addition, when describing representative embodiments, the specification may have presented the method and / or process as a specific sequence of steps. However, to the extent that the method or process does not rely on the specific order of the steps described herein, the method or process should not be limited to the steps of the specific order described. As will be understood by those of ordinary skill in the art, other sequences of steps are also possible. Therefore, the specific sequence of the steps set forth in the specification should not be interpreted as a limitation to the claims. In addition, the claims for the method and / or process should not be limited to the steps of performing them in the order written, and those skilled in the art can easily understand that these sequences can be changed and still remain within the spirit and scope of the embodiments of the present application.

[0033] The vane pump includes an impeller 100 and a casing. The impeller is disposed in the casing and is rotatably connected to the casing. The impeller can rotate around its own axis. The impeller can be connected to a motor, and the motor can drive the impeller to rotate.

[0034] like Figure 1 As shown, Figure 1An impeller 100 before blade modification in this embodiment is shown. The impeller 100 includes a hub 2, a rim 3 and a plurality of reference blades 1. The hub 2 is generally configured as a body of revolution and is disposed in the middle of the impeller 100. The hub 2 may be a body of revolution whose diameter gradually increases from one end to the other end. The rim 3 is configured as a roughly cylindrical shape. The diameter of the rim 3 gradually increases from one end to the other end. The rim 3 is sleeved outside the hub 2 and is coaxially arranged with the hub 2, and the ends of the hub 2 and the rim 3 with smaller diameters face the same direction. An annular gap is provided between the rim 3 and the hub 2. The diameter of one end of the annular gap is small, and the diameter of the other end is large. The reference blade 1 is disposed in the annular gap, and the plurality of reference blades 1 are evenly distributed around the hub 2. The reference blade 1 extends from the hub 2 to the rim 3. The reference blade 1 is provided with a first end and a second end. The first end and the second end are arranged opposite to each other: the end surface of the first end of the reference blade 1 is connected to the outer peripheral wall of the hub 2 , and the end surface of the second end of the reference blade 1 is connected to the inner peripheral wall of the rim 3 .

[0035] This embodiment also proposes a blade modification method for suppressing inter-blade rotational stall and improving cavitation performance. The blade modification method can improve the blades of the impeller 100, and the blade modification method includes the following steps:

[0036] Step S1: Obtain a model of a reference blade 1, and draw 2n+1 spanwise surface contour lines on the model of the reference blade 1, wherein the 2n+1 spanwise surface contour lines are arranged in sequence from a first end of the reference blade 1 connected to the hub 2 to a second end of the reference blade 1 connected to the rim 3, wherein the first spanwise surface contour line 4 is an edge line of an end surface of the first end of the reference blade 1, the 2n+1 spanwise surface contour line 5 is an edge line of an end surface of the second end of the reference blade 1, and 2n-1 spanwise surface contour lines are evenly drawn on the model surface of the reference blade 1 between the first spanwise surface contour line 4 and the 2n+1 spanwise surface contour line 5;

[0037] The reference blade 1 is the blade that needs to be modified. A model of the impeller 100 may be established in advance, and the model of the impeller 100 includes the model of the reference blade 1. The model of the reference blade 1 is a virtual model, and the model at least includes the outer contour shape of the reference blade 1.

[0038] like Figure 2As shown, 2n+1 spanwise surface contour lines are drawn on the model of the reference blade 1, where n is a positive integer greater than or equal to 1. The spanwise surface contour lines are closed annular lines. The 2n+1 spanwise surface contour lines are arranged side by side in sequence from the first end of the reference blade 1 to the second end of the reference blade 1, and two adjacent spanwise surface contour lines are spaced apart. The first spanwise surface contour line 4 is the edge line of the end surface of the first end of the reference blade 1, that is, the edge line of the interface between the first end of the reference blade 1 and the hub 2. The 2n+1 spanwise surface contour line 5 is the edge line of the end surface of the second end of the reference blade 1, that is, the edge line of the interface between the second end of the reference blade 1 and the rim 3. The 2nd to 2n-1th spanwise surface contour lines are all annular lines extending along the surface of the reference blade 1, extending from the leading edge of the reference blade 1 along one plate surface of the reference blade 1 to the trailing edge of the reference blade 1, and then extending along another plate surface of the reference blade 1 to the leading edge of the reference blade 1, forming a closed annular line. The leading edge of the reference blade 1 is the windward edge of the reference blade 1 , and the trailing edge of the reference blade 1 is the edge of the reference blade 1 opposite to the windward edge.

[0039] The 2nd to 2n-1th spanwise surface contour lines are located on the model surface of the reference blade 1 between the 1st spanwise surface contour line 4 and the 2n+1th spanwise surface contour line 5. The 2nd to 2n-1th spanwise surface contour lines divide the model of the reference blade 1 into 2n segments in the direction from the first end to the second end. The model of the reference blade 1 is divided into 2n-1 spanwise surface contour lines at equal intervals on the surface between the 1st spanwise surface contour line 4 and the 2n+1th spanwise surface contour line 5.

[0040] Step S2: increasing the overall spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 in the rotation direction of the reference blade 1, and the increase in the spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 is increased in sequence, and then entering step S3;

[0041] like Figure 3 As shown, before step S2, a rectangular coordinate system can be established in advance in a two-dimensional plane perpendicular to the rotation axis of the blade, the intersection of the rotation axis of the blade and the two-dimensional plane is the origin of the coordinate system, a horizontal axis X passing through the origin is set in the two-dimensional plane, and the spatial angle of any point on the spanwise surface contour line is the angle between the vector of the projection from the origin to this point on the two-dimensional plane and the horizontal axis X.

[0042] The point at the leading edge of the spanwise surface contour line is projected into the two-dimensional plane to form a leading edge point projection. The angle between the vector from the origin to the leading edge point projection and the horizontal axis X is the spatial angle θ at the leading edge of the spanwise surface contour line. 01 The point at the trailing edge of the spanwise surface contour line is projected into the two-dimensional plane to form a trailing edge point projection. The angle between the vector from the origin to the trailing edge point projection and the horizontal axis X is the spatial angle θ at the trailing edge of the spanwise surface contour line.02 .

[0043] The spatial angle of the entire spanwise surface contour line is increased toward the rotation direction of the reference blade 1, that is, the translation spanwise surface contour line is rotated as a whole around the rotation axis of the reference blade 1 toward the rotation direction of the reference blade 1. The increase in the spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 is increased successively, that is, the larger the angle of the overall rotation from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 around the rotation axis of the reference blade 1 toward the rotation direction of the reference blade 1 is, the greater the angle of the overall rotation from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5.

[0044] The spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 is increased toward the rotation direction of the blade, and the increase in the spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 is increased in sequence. Preferably, the increase in the spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line 5 is an arithmetic progression. For example, if the increase in the spatial angle of the second spanwise surface contour line is θ, then the increase in the spatial angle of the third spanwise surface contour line is 2×θ… The increase in the spatial angle of the 2n+1 spanwise surface contour line 5 is 2n×θ, and the angle θ is greater than zero.

[0045] When the spatial angle from the second spanwise surface contour line to the 2n+1th spanwise surface contour line 5 is increased, the spatial angle of each point from the leading edge to the trailing edge on any spanwise surface contour line is uniformly increased.

[0046] like Figure 4 As shown, the position of the first spanwise contour line 4 remains unchanged. Compared with the first spanwise contour line 4, the relative positions of the second to 2n+1 spanwise contour lines in space change, among which the 2n+1 spanwise contour line 5 is the most shifted in space.

[0047] Step S3: Using the 1st to 2n+1th spanwise surface contour lines 5 to fit a smooth surface through spline interpolation, the smooth surface is used as the outer contour of the modified blade 1a.

[0048] The smooth surface is fitted by using the unchanged first spanwise surface contour line 4 and the newly generated second spanwise surface contour line to the 2n+1th spanwise surface contour line 5, and the fitted smooth surface is used as the outer contour of the modified blade 1a. Keeping the position of the first spanwise surface contour line 4 unchanged can ensure that the placement position of the blade at the hub 2 remains unchanged.

[0049] like Figure 4 , 5 As shown in FIG. 1 , due to the increase in the spatial angle from the second spanwise surface contour line to the 2n+1th spanwise surface contour line 5 in the direction of blade rotation, the modified blade 1a is tilted forward in the direction from the hub 2 to the rim 3 in the direction of blade rotation, forming a forward-tilted blade. Figure 4 As shown, the forward tilt angle It is the difference between the leading edge space angle of the impeller blade near the wheel rim and the leading edge space angle of the blade near the wheel hub. This angle reflects the degree of overall forward tilt of the blade. When the leading tilt angle is 0°, the blade is a conventional vertical blade. The greater the leading tilt angle, the greater the forward tilt of the blade. In the present invention, the leading edge and trailing edge of the 2n+1 spanwise contour line simultaneously increase the space angle 2nθ. This blade modification method has the following advantages:

[0050] 1. The modification method is simple. The blade model modification can be completed by simply adjusting the leading edge and trailing edge space angles of the blade's different spanwise contour lines, which greatly simplifies the optimization process and improves production efficiency and work reliability;

[0051] 2. Wide applicability. Most existing flow optimization technologies attempt to modify the flow at the leading edge of the blade or in the bladeless area. At the same time, the interaction between multiple factors must be considered, and the process is relatively complicated. This application changes the relative position of the blade in space along the span direction, thereby changing the distribution characteristics of the flow in space, so as to achieve the effect of suppressing or delaying the rotational stall and the initiation of cavitation flow. This blade modification method can be widely used in the flow enhancement of vane pumps with diffusers;

[0052] 3. The axial flow channel of the blade itself, the inlet and outlet placement angles, and the wrap angles of the contour lines of each spanwise surface do not change, that is, the design operating point of the impeller itself does not change.

[0053] In an illustrative embodiment, in step S1 , 2n+1 spanwise contour lines are drawn on the reference blade 1 , where n is greater than 2.

[0054] n determines the number of spanwise contour line divisions and can determine the precision of the blade spanwise contour line division. The larger n is, the higher the precision of the blade spanwise contour line division. The minimum value of n is preferably 2, that is, the reference blade 1 should be divided into at least 5 sections along the span direction, and 5 spanwise contour lines are drawn on the reference blade 1, so as to ensure the accuracy of the modification.

[0055] In an exemplary embodiment, in step S2 , the increase in the spatial angle of the 2n+1th spanwise surface contour line 5 is greater than or equal to 28°.

[0056] The increase in the spatial angle of the 2n+1th spanwise surface contour line 5 is 2n×θ, and when the increase 2n×θ reaches 28°, the stall and cavitation initiation points can be significantly delayed, thereby suppressing or delaying the rotating stall and cavitation occurrence points, and improving the unsteady unstable flow phenomenon inside the unit.

[0057] This embodiment also proposes an impeller modification method, which includes all the steps of the blade modification method described above.

[0058] This embodiment also provides an impeller, which includes a modified blade 1a. The modified blade 1a uses the smooth curved surface obtained by the blade modification method as the outer contour.

[0059] In an illustrative embodiment, Figure 5 As shown, the impeller includes a hub 2, a rim 3 and a plurality of modified blades 1a. The hub 2 is generally configured as a body of revolution and is disposed in the middle of the impeller 100. The hub 2 may be a body of revolution whose diameter gradually increases from one end to the other end. The rim 3 is configured as a roughly cylindrical shape. The diameter of the rim 3 gradually increases from one end to the other end. The rim 3 is sleeved outside the hub 2 and is coaxially arranged with the hub 2, and the ends of the hub 2 and the rim 3 with smaller diameters have the same orientation. There is an annular gap between the rim 3 and the hub 2. One end of the annular gap has a small diameter and the other end has a large diameter. The modified blades 1a are disposed in the annular gap, and a plurality of modified blades 1a are evenly distributed around the hub 2. The modified blades 1a extend from the hub 2 to the rim 3. The modified blades 1a are provided with a first end and a second end, and the first end is arranged opposite to the second end. The end surface of the first end of the modified blade 1 a is connected to the outer peripheral wall of the hub 2 , and the end surface of the second end of the modified blade 1 a is connected to the inner peripheral wall of the rim 3 .

[0060] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0061] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include at least one of the features.

[0062] In the description of the present application, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0063] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0064] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0065] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0066] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A blade modification method for suppressing inter-blade rotational stall and improving cavitation performance, characterized in that: include: Obtain a model of a reference blade, and draw 2n+1 spanwise surface contour lines on the model, wherein the 2n+1 spanwise surface contour lines are arranged in sequence from a first end of the reference blade connected to a hub to a second end of the reference blade connected to a rim, wherein the first spanwise surface contour line is an edge line of an end surface of the first end, the 2n+1 spanwise surface contour line is an edge line of an end surface of the second end, and 2n-1 spanwise surface contour lines are evenly drawn on the model surface of the reference blade between the first spanwise surface contour line and the 2n+1 spanwise surface contour line; The overall spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line is increased toward the rotation direction of the reference blade, and the increase amount of the spatial angle from the second spanwise surface contour line to the 2n+1 spanwise surface contour line is increased in sequence; A smooth surface is fitted using the 1st to 2n+1th spanwise surface contour lines, and the smooth surface serves as the outer contour of the modified blade.

2. The blade modification method according to claim 1, characterized in that: The amount of increase of the space angle from the second spanwise surface contour line to the 2n+1th spanwise surface contour line increases in sequence in an arithmetic progression.

3. The blade modification method according to claim 1, characterized in that: The increase in the spatial angle of the 2n+1th spanwise surface contour line is greater than or equal to 28°.

4. The blade modification method according to claim 1, characterized in that: When the space angle of each spanwise surface contour line is increased, the space angle of each point of the spanwise surface contour line from the leading edge to the trailing edge increases uniformly.

5. The blade modification method according to claim 1, characterized in that: The 2nd to 2n-1th spanwise surface contour lines evenly divide the model of the reference blade into 2n segments in the direction from the first end to the second end.

6. The blade modification method according to claim 1, characterized in that: A rectangular coordinate system is established in a two-dimensional plane perpendicular to the rotation axis of the blade. The intersection of the rotation axis of the blade and the two-dimensional plane is the origin of the coordinate system. A horizontal axis X passing through the origin is set in the two-dimensional plane. The spatial angle of any point on the spanwise surface contour line is the angle between the vector of the projection from the origin to this point on the two-dimensional plane and the horizontal axis X.

7. The blade modification method according to claim 1, characterized in that: The position of the first spanwise surface contour line remains unchanged.

8. A method for modifying an impeller, characterized in that: The impeller modification method comprises the steps of the blade modification method according to any one of claims 1 to 7.

9. An impeller, characterized in that: Including modified blades; The modified blade adopts the smooth curved surface obtained by the blade modification method according to any one of claims 1 to 7 as its outer contour.

10. The blade modification method according to claim 9, characterized in that: The impeller further comprises a hub and a rim coaxially arranged with the hub, and two ends of the modified blade are respectively connected to the hub and the rim.

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